The role of water in the low-temperature hydrogen reduction of hematite into iron, and the role of the surface oxygen chemical potential in double reactions

The striking role played by water vapour during the low temperature reduction of hematite into magnetite by carbon monoxide has been reported but the possibility that this effect was not due to hydrogen produced from the H₂O+CO shift reaction had to be eliminated.

A very similar effect by water vapour during the reaction of hematite with hydrogen is reported, the nucleation of magnetite is more regularly distributed and the magnetite layer is much more regular, but the rate of reaction is lower.

As the reduction proceeds to give more iron, another striking effect is observed: in the presence of water, there is no overlap of the steps hematite → magnetite and magnetite → iron; the reduction of magnetite starts once the hematite has disappeared. It is shown that rather than being a problem of transfer through a stagnant film, the clearly different steps may be attributed to the fact that when adsorption-desorption is not fast enough, the surface oxygen chemical potential differs from that of the gas.